A listener emailed the old ruleyourpool email address (the new one is ruleyourpool@gmail.com) and brought up something interesting. He said "Nowhere in your RYP podcasts have I heard you mention that the LSI is not an index. It's a delta between the saturation pH and the current pH. LSI is the difference between the pH you have and the pH your water wants." Let's discuss this.
[00:00] - Intro
[01:44] - Wójtowicz Update to the LSI Formula
[04:21] - Dr. Langelier's Original Index Formula
[05:56] - What water wants vs. What air wants
[08:18] - Closing
190. Is the LSI actually an "index"?
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Eric Knight: Hey everybody, welcome back to the Rule Your Pool Podcast. I've got my glasses on. We are going to nerd out together today. And if this loses you and you unsubscribe from the show, so be it. Somebody who has been listening to this show reached out, uh, actually over a month ago, but it was just forwarded to me recently. Because he, he actually emailed the old email podcast@orendatech.com. I'm not there anymore. I can't see those. So if you do have any questions like this or any comments or suggestions for the show, it is ruleyourpool@gmail.com. That's how you can reach me now.
And so this was forwarded to me. It's a great topic. I had to beef up on it. I had to read it. And so that's why my glasses are on because we're going to be reading today. I've got my screen shared if you were watching on video. And for those of you listening at home, try to stay awake for this one. It won't be very long, but it's going to go a little bit deep. And I think part of the brand of this show is to not just be a social hour where we talk about stuff in the industry. Let's actually dig deep into the science.
And in full disclosure, I learned a lot researching this because I never actually went this deep. I mean, we had chemistry consultants who helped us with this and people who understood this. So I've been trying to understand this and I'm not quite there, but I think I have enough to distill it for an episode
And here's what he emailed me. He said, "Hi, Eric. I love your podcasts and I'm sorry to see you've moved on, but I do want to state that nowhere in your RYP, that's Rule Your Pool, podcasts, have I heard you mention that the LSI is not an index. It's the delta between the saturation pH and the current pH. LSI is the difference between the pH you have and the pH your water wants."
Wow. Okay. Awesome suggestion. So let's get into what that actually means.
[00:01:44] Wojtowicz Update to the LSI
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Eric Knight: Years ago, there were some questions as to how accurate the Orenda Calculator was because it differs from the charts, and you'll see in this article exactly why. Actually the charts are referenced down here somewhere. Um, this is the article that it's based on. It's actually several of them. So, uh, this goes into a lot of characters and equations that I don't even know how to speak because I don't know what the symbols mean.
But I'm sure if you had a PhD in chemistry or physics, you could probably understand it. But this is available on the Orenda website. You can also just search for it. I'm sure AI can find it. This came from the OnBalance website. So if you want to go to poolhelp.com, you can go through the entire catalog of this, which is called the Journal of the Swimming Pool and Spa Industry, Volume three, number one, pages 28 through 34.
This comes from 2001, and, .It is in depth. And so what I wanted to do here is visit what this email says.
So John here says that the LSI is not an index. It's the delta between the saturation pH and the current pH. Timeout. Let's go back to what Dr. Langelier did in 1936. And by the way, for those of you listening, if you don't already have a decent understanding of LSI, we talk about it pretty thoroughly in this show.
So you can go back and, I mean, the first, I say eight episodes, we're going to cover it a lot. But we have a whole bunch of episodes on this. The LSI essentially is the saturation equilibrium of calcium carbonate in the water. This is what we use to quantify the nebulous term balance in water.
There's water balance and there's water quality. Water quality is manmade. That's disinfection, keeping water safe, clean, clear, all that stuff. That has nothing to do with balance. Water balance is physics. So is the water happy? Basically, with whatever it's saturated with? And if it's not happy, it's going to pursue its own natural state.
And in the sense of balance that we're using with the LSI, if water is hungry for calcium, it's going to steal it from cement-based finishes because they're, well, they're calcium-based. This is a big topic in the swimming pool business. And so if you're new here, you probably wouldn't necessarily understand how complex this is going to get, but that's what this show is about, and I hope you stick around for other episodes anyway.
[00:04:21] Dr. Langelier's Original Index Formula
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Eric Knight: Okay, so we're going to go down here. I think this is the, uh, yeah, it's the second or third page. So Langelier Saturation Index formulation, and I quote, Langelier ... Oh, this comes from John Wojtowicz by the way, from that article I just cited.
Langelier, 1936, calculated the pH of saturation in unstabilized water using equation 5 (with S=1). He substituted alkalinity for bicarbonate and converted activities to concentrations by introducing ionic strength corrections. And the formula is pHs, meaning pH at saturation, equals the negative log of calcium ions, which is Ca2+, minus the log of alkalinity, minus the log of K2 divided by Ks.
Now, the K is the saturation constant, he goes through like a whole page explaining what those are. But the point is, what he's saying is the pH at saturation is not necessarily where your pH is right now. So he takes that to calculate what pHs, which is pH at optimal calcium saturation based on equilibrium constants, thermodynamics, et cetera. And the original LSI formula was this. It was pH actual minus pHS, which I just explained above.
So to that sense, John's email here is correct. The original Langelier Saturation Index was the delta between where your pH is and where the pH is optimal for the saturation equilibrium of calcium. Or as he puts it, and I like this, it's the difference between the pH you have and the pH your water wants.
[00:05:56] What Water Wants vs. What Air Wants
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Eric Knight: Ooh, I like that. Now, interestingly enough, it, it's what the water wants. That's not necessarily what the air wants. And as we talk about on this show, you have two different physics that you're up against. Probably a lot more than that actually. You've got the water physics, which is water getting to its natural state, getting back to LSI.
And then you've got air physics, which is Henry's Law, which wants to equalize carbon dioxide. Well, and every other gas, but CO2 determines pH here. So it, it wants to equalize CO2 in the water and CO2 in the air. So they don't necessarily talk to each other. But when you find equilibrium, it's a really special thing. That's about as complicated as we're going to get here.
If you want to read this, feel free. You can throw it into ChatGPT or Gemini or whatever and distill it down and get a better understanding of this. But what I want to get at here is he's correct in that the saturation index is the difference between where water wants that pH based on optimal calcium saturation versus where your pH is.
That's why 0.0 is perfect balance. Now, it doesn't always stay there. Of course, the pH is naturally going to rise. But again, if the LSI was not a delta, it would be some arbitrary number, right? But because it's plus or minus based on zero being perfect, that tells you it is the delta based on some standard.
And that standard is the optimal, in those current conditions, the optimal equilibrium for calcium carbonate. At the optimal alkalinity, at the optimal temperature, at the optimal amount of calcium carbonate, at the optimal ... Well, CYA corrects against alkalinity, So I, I guess we should have said carbonate alkalinity, but it's in those current conditions, where would the pH be for perfect calcium saturation? That's the pHs.
And how big of a difference are you away from that is the LSI. So I've never really looked at it this way. You know, I've just had it spit out values on the calculator and we know that we're trying to be between 0.0 and 0.3 if we want to be green. Certainly during a startup, we want to be 0.2 to 0.29.
We have found through a lot of trial and error that that is the best first five to six days, so that you're slightly positive on the LSI. But really anything between minus 0.30 to positive 0.30, you are close enough. And that seems to be holding true.
So I know this is a short episode and I hope I didn't lose you, but there is a lot of logic behind this and you are welcome to do your own research. I strongly encourage you do.
[00:08:18] Closing
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Eric Knight: But I think for most of the pool pros listening to this, you can trust the calculator because it's been working for you. This is the article right here that I just cited. You are welcome to read it yourself. This is the article that is the basis of the Orenda Calculator. It was not made up. It was not customized because Orenda wanted it this way. No, read it. You'll understand why we follow this logic and these numbers. We also have an article that I wrote when I was still with Orenda in, uh, ask.orendatech.com. Just type in calculator. And you will find, you know, I forget the name of it. I think it's, uh, why the Orenda calculator has different results than every other calculator.
Well, as far as I know, at least as of today, Orenda calculator is the only calculator that goes to this depth to use all of this. And we wanted it to be the most accurate calculator in the world to calculate LSI to help you in the field, and I believe we accomplished that. And you can read this for yourself and you can decide. But I just wanted to get through that.
Thank you, John, for reaching out. and allowing me to talk nerdy for a while. This was cool. And, and I've learned a lot. I do appreciate it. I read this a little bit more in depth.
This is the most accurate information available. You can trust in that and check our work, check our math. Because this is the math. It's not, um, it's not a secret. We've been open about it. Uh, but, you know, you got to have some pretty good technology to try to do this right. So that's why the routing softwares that are available in the industry are all using Orenda because they believe, just like I do, that we should have a standard way of measuring this very important factor, which is the LSI.
And since you can't just test it, you have to test a bunch of things, throw it into a calculator and get a number. And I hope this helps you out. And if you are thinking in terms of how you can best standardize your service business, so that you are constantly getting the right thing done every single week so that you can have predictable and therefore profitable water, it helps to know why the LSI is so important.
So again, John, he didn't put his last name in here, but John, thank you so much for the idea. Yes, it is the delta between your current pH and the optimal pH, and that's why it is based on 0.0. You're awesome. Thank you so much. And I have a few other listener emails here. Um, frankly, I don't know how to answer some of these questions, so I have been reaching out to people who do, and hopefully I can get them on the show soon.
If you have questions and episode suggestions for the Rule Your Pool Podcast, again, the email to get to me is ruleyourpool@gmail.com. I'm Eric Knight, director of Watershape University and your suboptimal host of this podcast. Thank you so much for listening, and we'll see you next time. Take care, everyone.